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Conference programme 

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Poster session

Lead Session Chair:
Stephan Barth, Managing Director, ForWind - Center for Wind Energy Research, Germany
Peter Petersen DONG Energy Wind Power, Denmark
Co-authors:
Peter Petersen (1) F P Jesper Holm Elkjær (1)
(1) DONG Energy Wind Power, Gentofte, Denmark

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Poster
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Presenter's biography

Biographies are supplied directly by presenters at OFFSHORE 2015 and are published here unedited

Peter Petersen holds a position as Chief Specialist within the Substation functional area in DONG Energy Wind Power and as such overall technical responsible for structural, LV, mechanical and utility for the transmission assets designed and build by DE Wind Power. Mr. Petersen has been working with offshore structures for the North Sea for more than 25 years, first within offshore oil&gas, and the past 12 years within offshore wind. He holds a M.Sc. in structural engineering from the Technical University of Denmark and has previously been project manager for the Borkum Riffgrund offshore substation installed in 2013

Abstract

'Optimised wind farm supply chain by introduction of distributed substations

Introduction

The offshore substation topside and foundation is typically contracted independently of the wind turbine, WTG, foundation contracts. The Distributed Substation philosophy offers a number of opportunities to merge offshore substation and foundation installation and fabrication contracts ultimately lowering both developer DEVEX cost and project CAPEX cost. The main savings are identified in the joint installation of WTG foundations and Substation and the development of a standard foundation both suitable for WTG’s and Substations topsides.

Approach

With the Distributed Substation topside being lighter (~1000 tonnes) than a typical offshore substation topside (~2000 tonnes) the basic foundation principles needs to be revisited. The large diameter monopiles or jackets applied for today’s WTG’s has been identified as a suitable foundation for the Distributed Substation. In the design phase efforts are put into making the substation foundation as similar to the WTG foundation as possible with the only deviations found in the interface to the topside. DONG Energy has already developed and installed the 3-legged jacket identified and proven suitable as the foundation for the Distributed Substation topside.

Main body of abstract

With a minimum of 2 substations per wind farm, focus is on making two identical topsides to ensure synergies in the fabrication phase.

By having this dual purpose foundation the scope of substation foundation supply is taken out of the normal offshore substation, OSS, contract and given to the WTG foundation fabrication contractor. The drivers for this are several; Fewer contracts to administrate by developer, participation in mass production set-up resulting in lower fabrication costs and a more simplified supply chain.

Typically the OSS’s with two transformers with 180-200 MVA rating are installed by Heavy Lift Vessels with lifting capacities in the range 2500-4000 mT. Vessels in this range typically operates in the oil and gas industry, resulting in an undesirable competition on vessel availability. The associated high day rates results in a relatively large part of the total offshore substation CAPEX to be driven by installation costs. With the Distributed Substations topology, only a single transformer and switchgear required for connection to the cables are installed per topside and together with other low voltage and structural system simplifications, the topsides will have a weight suitable to be lifted by a WTG foundation installation vessel with capacities 1200 – 1500 mT. This opens for the typical independent offshore substation installation contract to be taken out of the supply chain with the associated cost down effect. With the WTG foundation installation vessel being contracted for a long-term period a further flexibility in terms of timing for the offshore substation installation is introduced.


Conclusion

From a risk perspective the Distributed Substation concept has something to offer as well. The consequence of an critical event leading to business interruption may be less severe compared to the normal singular OSS concept. This is partly inherent in the concept by distribution of the transmission capacity on two or more platforms and may further be supported by the wind farm grid layout applied.


Learning objectives
DONG Energy sees the concept of Distributed Substations as a concept with potential for lowering cost of energy in general and has on a specific project been able to demonstrate the viability of the concept through a comprehensive desk study, feasibility design and supply chain analysis.